Expression of OmpC and OmpF porin proteins and survival of Escherichia coli under photooxidative stress in Black Sea water

In the present study, the synthesis of OmpC and OmpF porins (outer membrane proteins C and F, respectively) of Escherichia coli under photooxidative stress in Black Sea water and the roles of RpoS (the starvation/stationary phase sigma factor, sigma(38)) and EnvZ (a transmembrane environmental sensor protein) in changing porin protein expression were investigated. The t(99) (time required for a 2 log reduction) values for wild-type E. coli W3110 and MSZ31 (envZ(-)) under photooxidative stress were observed to be 14.3 and 16.8 h, respectively, while for porin-deficient mutants MKC505 (ompC(-)), MH621 (ompF(-)), MKCF36 (ompF(-)ompC(-)), and MSR31 (ompR(-)) they were 10.6, 10.2, 9.8 and 9.1 h, respectively. Further, when the porins or ompR were deleted, the resistance to photooxidative stress decreased. OmpC and OmpF porin expression increased in all studied transcriptional fusion strains (wild type and mutants) in control microcosms, and almost completely decreased under photooxidative stress in the test microcosms, which consisted of light exposure with methylene blue added as a photosensitizer. Thus, it could be concluded that RpoS and EnvZ regulation of the synthesis of OmpC and OmpF is not photooxidation-dependent. This study determined for the first time that the expression of ompC in brackish water is influenced by RpoS.